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sched/walt: Improve comments

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Document irqtime and cleanup window roll over explanation.

Change-Id: I2fc092dd07926e35b1bf2f1839d56aa396fc666f
Signed-off-by: Abhijeet Dharmapurikar <quic_adharmap@quicinc.com>
Signed-off-by: Ashay Jaiswal <quic_ashayj@quicinc.com>
This commit is contained in:
Abhijeet Dharmapurikar 2022-03-21 18:23:24 -07:00 committed by Rishabh Bhatnagar
parent 327df46119
commit df9aed75af
1 changed files with 54 additions and 1 deletions
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55
kernel/sched/walt/walt.c
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@ -1564,6 +1564,50 @@ static void rollover_cpu_window(struct rq *rq, bool full_window)
/*
* Account cpu activity in its
* busy time counters(wrq->curr/prev_runnable_sum)
*
* While the comments at the top of update_task_demand() apply, irqtime handling
* needs some explanation.
*
* Note that update_task_ravg() with irqtime is only called when idle, i.e. p is
* always idle
*
* ms_i = mark_start of idle task
* ws = wrq->window_start
* irq_s = start time of irq
* irq_e = end time of irq = wallclock
*
* note irqtime = irq_e - irq_s
*
* Similar to the explanation at update_task_demand() we have few sitautions for irqtime
*
* ws ms_i is ie
* | | | |
* V V V V
* --------|--------------------|
* prev curr
*
* In the above case, new_window is false and irqtime is accounted in curr_runnable_sum, this is
* done in the if (!new_window) block.
*
* ms_i ws is ie
* | | | |
* V V V V
* -------------|---------------------
* prev curr
*
* In this case, new_window is true, however the irqtime falls within the current window, the
* entire irqtime is accounted in curr_runnable_sum. This is handled in the if (irqtime) block and
* within that if (mark_start > window_start) block
*
* ms_i is ws ie
* | | | |
* V V V V
* --------------------|---------------
* prev curr
*
* In this case, new_window is true, portion of the irqtime needs to be accounted in
* prev_runnable_sum while the rest is in curr_runnable_sum. This is handled in the
* if (irqtime) block
*/
static void update_cpu_busy_time(struct task_struct *p, struct rq *rq,
int event, u64 wallclock, u64 irqtime)
@ -1641,8 +1685,16 @@ static void update_cpu_busy_time(struct task_struct *p, struct rq *rq,
}
/*
* situations below this need window rollover, which should already be done
* situations below this need window rollover,
* Rollover of cpu counters (curr/prev_runnable_sum) should have already be done
* in update_window_start()
*
* For task counters curr/prev_window[_cpu] are rolled over in the early part of
* this function. If full_window(s) have expired and time since last update needs
* to be accounted as busy time, set the prev to a complete window size time, else
* add the prev window portion.
*
* For task curr counters a new window has begun, always assign
*/
if (!p_is_curr_task) {
@ -1760,6 +1812,7 @@ static void update_cpu_busy_time(struct task_struct *p, struct rq *rq,
*/
WALT_PANIC(!is_idle_task(p));
/* mark_start here becomes the starting time of interrupt */
mark_start = wallclock - irqtime;
/*